A conventional door closer as shown in FIG. 14 comprises: an outer tube (T) fixed on a door frame (Df) and having an air hole (H) formed in a head portion of the door closer; a rod member (R) slidably moving in the outer tube (T) and secured to a door (D) opening from (or closing to) the door frame (Df); and a restoring spring (S) secured between the rod member (R) and the head portion of the outer tube (T); whereby upon pulling the rod member (R) and the door (D) to be separated from the door frame (Df), the air may be sucked into the tube (T) through the air hole (H) to fill the chamber in the tube (T); and when closing the door (D) by releasing the rod member (R), the air will be expelled or vented outwardly through the air hole (H) to retract the rod member (R) to approximate the door frame in order to close the door automatically as restored by the restoring spring (S).
However, such a prior art has the following drawbacks:    1. Only one tiny air hole (H) is provided so that it requires a great force to pull the rod member (R) outwardly when opening the door in order to overcome the vacuum force as existing in the chamber within the tube (T) when pulling such rod member (R), thereby easily causing the user tiredness.    2. When it is intended to temporarily keep the door at an opening state, the door, as lacking of temporary braking or stopping mechanism, will be automatically restored, once opened, as restored by the restoring spring to immediately close the door, thereby causing inconvenience for the user if he or she wants to come in or go out through the door by repeatedly opening the door.    3. When the door is restored to close by the spring (S), the rod member (R) as urged by the spring (S) may impact the related parts or elements of the conventional door closer to cause noise or may even damage the door closer due to the inertia force when resiliently restored or retracted to close the door.
The present inventor has found the drawbacks of the conventional door closer and therefore invented the door closer as lightly opened and bufferably closed.